The invention relates to the use of filamentous fungi in an immobilized system for the production of biopolymers, in particular polysaccharides. Further, the invention relates to the use of filamentous fungi for the production of polysaccharides wherein the fungi is fixed and anchored onto the surface of a porous, non-particulate support to form an immobilized cell system.
Polysaccharides, in particular scleroglucan has been typically produced from filamentous fungi by submerged cultures in batch stirred tank fermentors. However, the high viscosity in the system which is the result of cell growth and product formation, limits the conversion efficiency of the fermentation process. As the viscosity of the fermentation system increases during the batch operation, the conversion of glucose to polysaccharides is reduced. High viscosity and biomass cause many operational problems, and results in high product costs. Thus, it is advantageous to discover new more efficient processes to produce biopolymers, in particular polysaccharides, from filamentous fungi.
Cultivation of filamentous fungi has many difficulties associated with it due to the viscosity associated with the biomass and products produced. Typical cell immobilization techniques for filamentous fungi are entrapment procedures employing calcium alginate carrageen and the like. Atkinson et al., U.S. Pat. No. 4,582,600 describes an apparatus for the growth of biomass via entrapment in a reticulate multiple support structure with substantial voidage. These typical techniques are of limited utility with filamentous fungi because in viscous fungal systems the small multiple supports become overgrown resulting in poor mass transfer in the fermentation. Further, a proportionately higher percentage of the glucose will be converted to biomass in such a system.
As a result there has been an interest in employing immobilization techniques for the production of biochemicals and transformation of biochemicals in living systems. Immobilization techniques have been used for biopolymer production from microorganisms, see U.S. Pat. No. 4,384,044. However, there has not been successful use of immobilization techniques for the production of high molecular weight biopolymers from filamentous fungi.
It has been discovered by the instant invention that the passive immobilization of filamentous fungi onto a fixed support is well-suited for the production of biopolymers. The use of a porous, non-particulate support provides a mycelial surface that is exposed to but not contained in the nutrient medium. Further, in the process of the instant invention the fungal filaments are anchored to the surface of the support and thus the viscosity contribution from the biomass is decreased and the biopolymer product is freely secreted into the medium. The overall viscosity of the system is lower than that in a non-immobilized system and there is increased cell concentration within the bioreactor leading to higher overall productivity.
It is an object of this invention to produce a biopolymer from a filamentous fungi in an immobilized cell system wherein the fungi are fixed to a support. It is another object of the instant invention to optimize growth conditions for filamentous fungi in an immobilized system. It is another object of the invention to produce polysaccharides, in particular scleroglucan from filamentous fungi in a fixed immobilized bioreactor system with decreased overall viscosity. It is another object of this invention to utilize the rigid immobilized system in batch, semi-batch and continuous fermentation models to optimize process efficiency.
These and other objects, together with the advantages over known methods shall become apparent from the specification which follows and are accomplished by the invention as herein described and claimed.